Fuel cells have been used as a power source in many applications. For example, fuel cells have been proposed for use in electrical vehicular power plants to replace internal combustion engines. In proton exchange membrane (PEM) type fuel cells, hydrogen (or a gas containing hydrogen) is supplied to an anode side of the fuel cell and oxygen is supplied as an oxidant to a cathode side. The oxygen can be either a pure oxygen (O2) or air. The oxidant and hydrogen may be referred to separately as a “reactant” or collectively as the “reactants”. PEM fuel cells include a membrane electrode assembly (MEA) having a thin, proton transmissive, non-electrically conductive, solid polymer electrolyte membrane having the anode catalyst on one face and the cathode catalyst on the opposite face. If a diffusion medium (DM) and/or a barrier layer is bonded to the MEA and optionally sealed with a gasket as a unit, the unit is known as a unitized electrode assembly (UEA). To form a single fuel cell, a MEA or a UEA is disposed between a unipolar plate assembly or a bipolar plate assembly.
Bipolar plates include an anode side and a cathode side for adjacent fuel cells in the fuel cell stack. FIG. 1 illustrates an anode side 100 of a fuel cell plate 110 as known in the art. The fuel cell plate 110 is formed from a pair of unipolar plates coupled together by a welding process, or an adhering process, for example. Flow channels 112 are provided on the anode side 100 of the fuel cell plate 110 to facilitate the flow of hydrogen to the anode side 100 of each MEA or UEA. Flow channels are provided in the cathode side of the fuel cell plate 110 to facilitate the flow of oxygen to the cathode side of the MEA or UEA. The fuel cell plate 110 is made of a conductive material, such as a coated or treated stainless steel, so that the fuel cell plate 110 may conduct the electricity generated by the fuel cells. Additionally, the unipolar plates forming the bipolar fuel cell plate 110 define coolant flow channels (not shown) therebetween to facilitate the flow of a cooling fluid therethrough to control the temperature of the fuel cell plate 110 during use. Cooling fluid flowing through the coolant flow channels may warm up the fuel cell plate 110 during a startup process in below-freezing conditions. The coolant flow channels are typically parallel to the flow channels 112 formed on the anode side 100 and the cathode side of the fuel cell plate 110 within an active area of the cell.
The fuel cell plate 110 includes an inlet aperture 118 and an outlet aperture 120 to facilitate the flow of the hydrogen across the fuel cell plate 110. The fuel cell plate 110 also includes an inlet aperture 116 and an outlet aperture 114 to facilitate the flow of the oxygen across the fuel cell plate 110. The fuel cell plate 110 also includes a coolant inlet 124 and a coolant outlet 122 to facilitate the flow of coolant between the unipolar plates forming the fuel cell plate 110. A plurality of individual fuel cell plates like the fuel cell plate 110 of FIG. 1 is typically bundled together to form a fuel cell stack. The inlet apertures, 116, 118, 124 of each of the fuel cell plates 110 cooperate to form an oxygen inlet manifold, a hydrogen inlet manifold, and a coolant inlet manifold, respectively, and the outlet apertures 114, 120, 122 of each of the fuel cell plates 110 cooperate to form an oxygen outlet manifold, hydrogen outlet manifold and a coolant outlet manifold, respectively. A weld seam 126 formed between the inlet aperture 118 and the coolant outlet 122 and a weld seam 128 formed between the outlet aperture 120 and the coolant inlet 124 each forms a fluid tight seal between the inlet aperture 118 and the coolant flow channels, and between the outlet aperture 120 and the coolant flow channels. Additional weld seams (not shown) may be formed between the unipolar plates of the fuel cell plate 110 to create a hermetically sealed coolant section and to militate against the loss of the reactant and/or the coolant to the atmosphere.
In use, coolant is caused to flow through the coolant manifold and into the coolant inlet 124 of each of the fuel cell plates 110 of the fuel cell stack. The coolant is caused to flow through the coolant flow channels formed between the unipolar plates. The pressure of the coolant is sufficient to cause the coolant to flow into each coolant flow channel that is parallel to the flow channels 112. The flow of coolant is shown generally by arrows 130.
The fuel cell plates 110 of the stack are commonly arranged in electrical series. Each cell within the stack may include a UEA, and each UEA provides an increment of voltage. A group of adjacent cells within the stack is referred to as a cluster. A typical arrangement of multiple cells in a stack is shown and described in commonly owned U.S. Pat. No. 5,763,113, hereby incorporated herein by reference in its entirety.
After the fuel cell stack has been in operation and subsequently powered down in freezing atmospheric conditions, condensation in the flow channels 112 of the fuel cell plates 110 may form ice. The ice may accumulate in the flow channels 112 and in inlet ports 132, inlet tunnels 133, in outlet ports 134, and outlet tunnels 135. The inlet ports 132 are in fluid communication with the inlet tunnels 133 formed intermediate the unipolar plates that provide fluid communication between the inlet aperture 118 and the flow channels 112. The outlet ports 134 are in fluid communication with the outlet tunnels 135 formed intermediate the unipolar plates that provide fluid communication between the outlet aperture 120 and the flow channels 112. When the fuel cell stack is powered up in the freezing conditions, ice formed in the flow channels 112, the ports 132, 134, and the tunnels 133, 135 must be melted before the reactants may flow across the fuel cell plates 110. Once the ice has melted, the fuel cell stack may function properly and efficiently. Coolant at a temperature greater than freezing flowing through the inlet aperture 124 of each plate 110 of the stack will eventually melt the ice in the ports 132, 134 and the tunnels 133, 135 to facilitate the flow of reactant therethrough, thereby facilitating the startup of the fuel cell stack. An amount of time required to melt the ice in the ports 132, 134 and the tunnels 133, 135 with the flow of coolant will delay the startup and efficient operation of the fuel cell stack. To hasten the amount of time, an auxiliary heater may be used to increase a temperature of the coolant, thereby increasing a cost and a complexity of the fuel cell stack.
It would be desirable to develop a fuel cell plate having a coolant flow channel formed therein, at least a portion of the coolant flow channel disposed adjacent a reactant inlet to facilitate a melting of ice formed on the fuel cell plate and to minimize a startup time of a fuel cell stack incorporating the fuel cell plate.